The present invention relates to printing plastics substrates and in particular to printing plastics substrates, such as markers for identifying electric cables etc., using a thermal transfer printing process.
U.S. Pat. No. 5,676,478 discloses a printer for printing plastics tubular markers for applying to individual cables. These plastics tubular markers may be heatshrinkable or non-heatshrinkable. The printer comprises a thermal print head having an array of pixels, each of which can be thermally activated, in order to melt the surface of the plastics tubular markers and to form a corresponding image thereon. This process is slow because the plastics tubular markers have to be advanced sufficiently slowly for and image to be formed. The process is also unreliable, because the print head is liable to become clogged with melted plastics material.
It is known to print onto plastics by applying pressure and heat to a printing ribbon registering against the plastics material, such that a print composition carried by the ribbon is transferred to the material. Conventionally, thermal transfer ribbons rely upon a wax or resin to transfer the dry ink onto the feedstock substrate.
This method of printing has inherent drawbacks; for example, the ink can be removed by means of heat, chemical action or abrasion. This can result in important printed images becoming unreadable. Furthermore, over time, the action of ultra violet radiation on pigments in the ink can result in the image fading.